Managing Air in Compost

Most of the organisms that decompose organic matter are aerobic—they need air to survive. As the pile decays, the air inside the pile is consumed and the rate of decomposition declines. Bacteria that require less air to function take over. These bacteria work more slowly than aerobic bacteria. That’s why a pile that’s never turned and doesn’t have some other way of gaining access to air takes such a long time to decay.

Techniques for introducing air into a compost pile include turning the pile, making air vents, and using aerating tools.

Turning the pile

Although turning a compost pile offers several benefits, such as redistributing the organisms, the primary benefit is to provide air to all parts of the pile, thus dramatically increasing the rate of decomposition. For directions for turning, and knowing when to turn, see Turning Compost.

Air vents

Many inventive home composters have searched for a way to get air into the middle of a compost pile without having to turn the pile. The solution is to find some device that can be inserted into the pile to allow air to flow to the central core. Here are a few methods that are reportedly successful:

When building a freestanding compost pile, place two or three sturdy poles across the pile at the halfway point and then again when the pile is three quarters built. The materials will settle in a month or two. To aerate the pile, simply shake the end of each pole every month or so. That movement allows air to pass down the length of the pole. The microbial activity in the area around the poles will increase with each new supply of air.

Some composters employ a refinement of the pole-shaking technique. They use bamboo poles split down one side. When the hollow poles are shaken, the splits open a bit, allowing air into the center of the pile.

To get air into an enclosed pile, set a PVC pipe vertically in the center of the pile. Before placing the pipe, which should be at least 1 inch in diameter, drill holes randomly along the length. Load the compost into the bin around the pipe. Some home composters have used three or four aerating pipes set strategically in the pile. An 18-inch length of snow fencing, rolled tightly, can be used instead of PVC pipe.

Another alternative is to build the pile on a wood pallet or on a plastic aeration mat, which is available from some composting equipment suppliers. When you combine a pallet or mat on the bottom of the pile with some kind of a vertical pipe up the middle, you can produce finished compost in only a few weeks—without turning the pile once.

Tools for Aerating

Composting equipment suppliers offer a tool designed especially to introduce air without turning the pile. An aerating tool is a pole approximately 4 feet long. You insert the pole deep into the pile and tug at it, causing the paddles at the end to open. These attachments move the organic materials around a bit, allowing air to get into the center of the pile. The tool works best in a loose pile—you won’t be able to insert the pole very far into compressed material.